html, body {
  font-size: 16px;
}

.box {
  width: 100px;
  height: 100px;
  margin: 20px auto;
  background-color: orange;
}

span {
  position: absolute;
  top: 140px;
  left: 50%;
  transform: translate3d(-50%, 0, 0);
  letter-spacing: 2px;
  line-height: 24px;
}